This invention relates to imaging materials. In a preferred form, it relates to nacreous voided photographic reflective paper.
Prior art reflective imaging output materials such as silver halide reflective images or inkjet reflective images typically comprise imaging layers applied to a white reflective base material. The white reflective base reflects ambient light back to the observer""s eye to form the image in the brain. Prior art base materials typically utilize white reflecting pigments such as TiO2 or barium sulfate in a polymer matrix to form a white reflective base material. Prior art reflective photographic papers also contain white pigments in the support just below the silver halide imaging layers to obtain image whiteness and sharpness during image exposure, as the white pigment reduces the amount exposure light energy scattered by the cellulose paper core. Details on the use of white pigments in highly loaded coextruded layers to obtain silver halide image sharpness and whiteness are recorded in U.S. Pat. No. 5,466,519.
In U.S. Pat. No. 6,146,744 (Freedman) high aspect ratio filler particles are added to composite facestock and liner sheets to provide increased mechanical stiffness compared to polymer facestock and liner materials that do not contain filler particles. While high aspect ratio filler particles added to the base layer in an amount between 5% to 40% by weight does improve the stiffness of the liner and facestock, the filler particles do not provide a nacreous appearance. Further, the high aspect ratio particles are added to the core of the facestock and liner and not to the printed layers. It has been shown that high aspect ratio particles added to the core of a facestock do not provide adequate multiple reflection planes in combination with a dye based imaging system to provide the desired nacreous appearance. High aspect ratio particles provide a nacreous appearance when they are located adjacent to the dye based imaging layers. Further, not attempt was made to improve the reflectivity of the high aspect ratio particles and thus are not suitable for the formation of photographic images.
It has been proposed in U.S. Pat. No. 5,866,282 (Bourdelais et al) to utilize a composite support material with laminated biaxially oriented polyolefin sheets as a photographic imaging material. In U.S. Pat. No. 5,866,282, biaxially oriented polyolefin sheets are extrusion laminated to cellulose paper to create a support for silver halide imaging layers. The biaxially oriented sheets described in U.S. Pat. No. 5,866,282 have a microvoided layer in combination with coextruded layers that contain white pigments such as TiO2 above and below the microvoided layer. The composite imaging support structure described in U.S. Pat. No. 5,866,282 has been found to be more durable, sharper and brighter than prior art photographic paper imaging supports that use cast melt extruded polyethylene layers coated on cellulose paper.
It has been proposed in U.S. Pat. No. 6,071,680 (Bourdelais et al) to utilize a voided polyester sheet coated with light sensitive silver halide imaging layers for use as photographic output material. The voided layer in U.S. Pat. No. 6,071,680 improves opacity, image lightness, and image brightness compared to prior art polyethylene melt extrusion coated cellulose paper base materials. The image base proposed in U.S. Pat. No. 6,071,680 also contains an integral polyolefin skin layer to facilitate imaging layer adhesion at the time of manufacture and during the processing of silver halide imaging layers.
There, however, remains a continuing need for improvements to the appearance of imaging output materials. It has been shown that consumers, in addition to reflective output material, also prefer nacreous images. Nacreous images exhibit a pearly or nacreous luster, an iridescent play of colors, and a brilliant luster that appears in three dimensions. Nacreous appearance can be found in nature if one examines a pearl or the polished shell of Turbo marmoratus.
A nacreous photographic element with a microvoided sheet of opalescence is described in U.S. Pat. No. 5,888,681 (Gula et al). In U.S. Pat. No. 5,888,681 microvoided polymer sheets with microvoided polymer layer located between a cellulose paper base and developed silver halide imaging provide an image with an opalescence appearance. The nacreous appearance is created in U.S. Pat. No. 5,888,681 by providing multiple internal reflections in the voided layer of the polymer sheet. While the opalescence appearance is present in the image, the image suffers from a loss of image sharpness or acutance, a higher density minimum position, and a decrease in printing speed compared to a typical photographic image formed on a white, reflecting base. It would be desirable if the opalescent look of the image could be maintained while improving printing speed, increasing sharpness, and decreasing density minimum. Also, while the voided polymer does provide an excellent nacreous image, the voided layer, because it is pre-fractured, is subjected to permanent deformation, thus reducing the quality of the image.
In addition to the use of white pigments in reflective consumer photographs, white pigments are also utilized in photographic display materials for diffusion of illumination light source. While the use of white pigments in display materials does provide the desired diffusion and reflection properties, the white pigments tend to change the hue angle of the color dyes in a developed photographic display image. Dye hue angle is a measure in CIElab color space of that aspect of color vision that can be related to regions of the color spectrum. For color photographic systems there is a perceptual preferred dye hue angle for the yellow, magenta, and cyan dyes. It has been found that when photographic dyes are coated on support containing white pigments, the hue angle of the developed image changes compared to the hue angle of the dyes coated onto a transparent support. The hue angle change of photographic dyes caused by the presence of white pigments often reduces the perceived quality of the dyes compared to the dye set coated on a transparent base that is substantially free of white pigments. It would be desirable if a developed photographic dye set coated on a reflective support material had a dye hue angle that was not significantly different than the same dye set coated on a transparent support.
Nacreous pigments added to a matrix, such as paint or plastic, have been known to exhibit a nacreous appearance. The prior art use of the nacreous pigments have been for pigmenting paints, printing inks, plastics, cosmetics, and glazes for ceramics and glass. Nacreous pigments are dispersed in a matrix and then painted or printed onto a substrate. Pearl luster pigments containing titanium dioxide have been successfully employed for many years. They are constructed in accordance with the layer substrate principle, with mica being employed virtually without exception as substrate.
Mica pigments are used widely in the printing and coating industries, in cosmetology, and in polymer processing. They are distinguished by interference colors and a high luster. For the formation of extremely thin layers, however, mica pigments are not suitable, since the mica itself, as a substrate for the metal-oxide layers of the pigment, has a thickness of from 200 to 1200 nanometer. A further disadvantage is that the thickness of the mica platelets within a certain fraction defined by the platelet size in some cases varies markedly about a mean value. Moreover, mica is a naturally occurring mineral which is contaminated by foreign ions. Furthermore, technically highly complex and time-consuming processing steps are required including, in particular, grinding and classifying.
Pearl luster pigments based on thick mica platelets and coated with metal oxides have, owing to the thickness of the edge, a marked scatter fraction, especially in the case of relatively fine particle-size distributions below 20 micrometers. As a substitute for mica, it has been proposed to use thin glass flakes which are obtained by rolling a glass melt with subsequent grinding. Indeed, interference pigments based on such materials exhibit color effects superior to those of conventional, mica-based pigments. Disadvantages, however, are that the glass flakes have a very large mean thickness of about 10-15 micrometers and a very broad thickness distribution (typically between 4 and 20 micrometers), whereas the thickness of interference pigments is typically not more than 3 micrometers.
In U.S. Pat. No. 5,340,692 (Vermeulen et al) an imaging receiving material with nacreous pigment for producing contone images according to the silver salt diffusion process is disclosed. According to the process disclosed in U.S. Pat. No. 5,340,692, contone images with an antique look can be obtained utilizing the silver salt diffusion transfer process without the need of special processing liquids using a nacreous pigment in the imaging receiving layer or located between the support and the image receiving layer. The silver halide imaging layers used are created with retained silver and, therefore, are not semitransparent. Because the nacreous pigments used are contained in the imaging receiving layer and not silver halide imaging layer, the image form will not have a uniform nacreous appearance, as the density of the transferred silver halide image block the multiple reflections from the nacreous pigments. Further, the nacreous pigments utilized are too large and in too great a concentration to be included in the silver halide imaging layer as a rough surface would result, reducing the desired nacreous appearance of the image. The gold flakes used in the example in U.S. Pat. No. 5,340,692 are an attempt to simulate prior art black-and-white photographic xe2x80x9cSepatonexe2x80x9d appearance produced during a post process treatment of the imaging layers. While the image in the example does have an antique appearance, the image does not have a nacreous appearance.
In U.S. Pat. No. 4,269,916 (Bilofsky et al) and related patents U.S. Pat. No. 4,288,524 and U.S. Pat. No. 4,216,018, instant photographic products having reflective layers which comprise lemellar interference pigments are disclosed. The intended use of the lemellar pigments is to create a pleasing white reflective appearance for the base material without the need for blue tints. It has been proposed that flat particles of metal oxides created by coating salts with metal oxides and later dissolving the salts leaving a thin flake of metal oxide as a substitute for spherical TiO2 particles. Titanium dioxide particles typically are utilized in photographic art to create a white reflective surface for the viewing of print materials. The intent of U.S. Pat. No. 4,269,916 is to provide a white reflecting surface that does not have an angular viewing appearance and a consistent L*, thus the invention materials do not exhibit a nacreous appearance. Examples in U.S. Pat. No. 4,269,916 show high reflectivity at a variety of collection angles which is opposite of a nacreous appearance where reflectivity changes as a function of collection angle. Further, the lemellar pigments are not present in the silver halide imaging layers or in the base materials used in the invention.
In U.S. Pat. No. 5,858,078 (Andes et al), a process for the production platelet like, substrate free TiO2 pigment is disclosed for use in printing inks, plastics, cosmetics and foodstuffs is.
In U.S. Pat. No. 5,733,658 (Schmid et al) luster pigments obtainable by treating titania coated silicate based platelets from 400xc2x0 C. to 900xc2x0 C. with a gas mixture comprising a vaporized organic compound and ammonia are described as useful for coloring paints, inks, plastics, glasses, ceramic products, and decorative cosmetic preparations.
When imaging supports are subject to variations in ambient conditions over long periods of time, the image-containing layers and resin layers tend to deteriorate into a mass of cracks which are aesthetically undesirable and which, in extreme cases, extend over the entire print completely destroying the image. All polymers are inherently prone to chemical degradation that leads to loss of mechanical properties. They undergo thermal degradation during processing such as extrusion of thin films, and photooxidative degradation with long-term exposure to light. The TiO2 utilized in U.S. Pat. No. 5,858,078 and U.S. Pat. No. 5,733,658 catalyzes and accelerates both thermal and photooxidative degradation. In the art of resin coating imaging papers, the melt polymers are extruded at high temperatures and are also subjected to high shear forces. These conditions may degrade the polymer, resulting in discoloration and charring, formation of polymer slugs or xe2x80x9cgelsxe2x80x9d, and formation of lines and streaks in the extruded film from degraded material deposits on die surfaces. Also, thermally degraded polymer is less robust than non-degraded polymer for long-term stability, and may thereby shorten the life of the print.
It has been shown that when imaging layers such as silver halide, ink jet, flexography, and laser toner are applied to nacreous base materials, the nacreous appearance of the image is optimized when the image forming layers contain semitransparent dyes. The use of pigmented inks and dyes in the imaging layers tend to reduce the nacreous appearance of the image. In U.S. Pat. No. 6,071,654 (Camp et al) silver halide imaging layers that are semitransparent are coated on a nacreous support containing a voided polymer layer. The voided polymer layers create flat platelets oriented parallel to each other. The reflection, which reaches the eye, is primarily specular. It arises in depth, since each transparent polymer platelet reflects some of the incident light and reflects the remainder. The images in U.S. Pat. No. 6,071,654 exhibit a nacreous appearance.
There is a need for a reflective imaging material that provides a nacreous or pearlescent appearance that provides a good photographic image.
It is an object of the invention to provide improved photographic materials.
It is another object to improved image appearance compared to prior art voided base photographic materials.
It is a further object to provide photographic materials that have a nacreous appearance independent of the base material.
These and other objects of the invention are accomplished by an imaging element comprising at least one layer of oriented polyolefin and nacreous pigment.
The invention provides brighter, snappy images that have a nacreous appearance while having exceptional photographic sharpness and exposure speed.